Eastbound Pennsylvanian on Horseshoe Curve, 2016. — Amtrak: History of America's Railroad

45 years of Amtrak locomotives

File:Amtrak Pennsylvanian on Horseshoe Curve (8991394046).jpg - Wikipedia

Altoona's Horseshoe Curve: A Railroad Engineering Marvel

World Famous Horseshoe Curve

21 Horseshoe Curve Pennsylvania Stock Photos, High-Res Pictures, and Images - Getty Images

Up and Down and 'Round and 'Round and Back Again

Keystone Corridor - Wikipedia

History Blog

Early Amtrak trains in color

Keystone Corridor - Wikipedia

View of the Rockville Bridge and Susquehanna River, 2016. — Amtrak: History of America's Railroad